Special Containment Procedures: SCP-2735-1 and SCP-2735-3 are to be kept in a transparent airtight glass container filled with fresh water, at least 10 meters cubed, reinforced with steel bars. The water in this container should be continuously aerated with a mixture of hydrogen gas and carbon dioxide. 25% of this water should be drained and replaced weekly. Cultures of anaerobic autotrophic bacteria and archaea are maintained within this container1 for the purpose of feeding SCP-2735-1 and SCP-2735-3. If this container is damaged, SCP-2735-1 and SCP-2735-3 are to be relocated to a secondary container of the same design.

SCP-2735-4 is to be kept in a separate container, designed to the same specifications aside from being smaller, measuring at least 3 meters cubed and lined with foam padding. SCP-2735-4 is to be kept isolated from SCP-2735-1 and SCP-2735-3 at all times. A waterproof closed-circuit camera is placed within the container. A lamp is to be mounted to the top of the container to aid in sustenance for SCP-2735-4. SCP-2735-4 may be relocated to SCP-2735-1 and SCP-2735-3''s secondary container if its primary container is damaged, but SCP-2735-4 should not be within it at the same time as SCP-2735-1 or SCP-2735-3.

Various space observatories have been co-opted by the Foundation to determine the location of possible SCP-2735 artifacts in solar orbit. In the event of an SCP-2735 artifact being discovered, a standard Foundation retrieval team will be sent into orbit to recover the object(s). Under the unlikely circumstances that there is a surviving SCP-2735 instance onboard an object, that object is to be transferred into an orbit around earth and de-orbited, so the surviving instance can be relocated to the primary SCP-2735 containment unit.

SCP-2735-2''s remains are preserved in Secure Containment Locker 2735. Those who wish to access SCP-2735-2 should submit a request to Site Command prior to their research.

Description: SCP-2735 is a species of sapient aquatic organisms of which there are three surviving members. SCP-2735 is believed to have been dominant on Earth roughly 2.4 billion years ago, but was rendered functionally extinct. SCP-2735 are obligate anaerobes that consume carbon dioxide and produce methane, and will become physically ill when exposed to oxygenated air or water, resulting in death if exposed for extended periods.

SCP-2735 have their body structures arranged trilaterally. SCP-2735 instances range in length from roughly 1.5 to 3 metres long, and from roughly 0.5 to 1.75 metres in diameter, with the majority of their forms being taken up by a long tail. SCP-2735 instances primarily interact with objects using three appendages located on the anterior of their bodies, which each further split into five secondary appendages intended for grasping. Each SCP-2735 instance possesses a single compound eye located on the anterior of their body, covered by a translucent layer of skin. A circular, toothless mouth is located on the proximal end of each of an SCP-2735''s three primary appendages. The internal body plan of SCP-2735 resembles that of members of the phylum Echinodermata2, but is almost certainly unrelated. SCP-2735 instances are autotrophic and heterotrophic, and derive sustenance from both filtering microscopic organisms from water ingested through their three mouths and collecting sunlight using a dense coating of wire-like fibres on the posterior of their bodies. Skin colour in SCP-2735 instances vary between dark greens and browns, though it is possible that colouration was more varied among the larger population prior to its destruction. SCP-2735 lives in symbiosis with bioluminescent prokaryotes, which they are capable of altering the colour of. SCP-2735 instances have extremely thin and porous skin. This allows for cutaneous gas exchange, which is their only method of respiration, and causes the bioluminescent organisms in their blood vessels to be extremely visible. SCP-2735''s method of communication has not been translated by the Foundation as of yet, but appears to involve complex patterns of bioluminescent light.

Discovery: The initial four SCP-2735 instances were preserved in an advanced space station in a 90 degree retrograde solar orbit. A radio signal from the station was discovered by the Big Ear radio telescope in 1998, and subsequently intercepted by the Foundation. The signal was initially assumed to be alien in origin, until Foundation astronauts were able to enter the craft and study the preserved organisms, identifying them as terrestrial. The station used by the SCP-2735 instances was transferred to a terrestrial orbit and subsequently de-orbited, then used as temporary containment for SCP-2735 until Foundation researchers could learn more about the subject''s biology, at which point they were relocated to their current containers. After the initial finding, other SCP-2735 space stations were discovered in similar orbits, however all instances of SCP-2735 have either perished from the extended time in orbit or damage taken by collisions with other orbiting objects.

Incident-2735-A: On ██/██/19██ at 6:34 pm, the rate and luminosity of all four SCP-2735 instance''s bioluminescent emissions dramatically increased. This was noted, but not initially considered to be significant by observing personnel. At 6:42, the four SCP-2735 instances began repeatedly propelling themselves against a specific location on the primary containment chamber''s wall. This was recognized as a coordinated attempt to breach containment and Foundation agents entered the chamber.

At 6:47, as five (5) agents attempted to restrain the SCP-2735 instances, SCP-2735-2 succeeded in breaching the wall of the chamber. SCP-2735-2 and the other instances were violently forced out of their containment chamber by the resulting flow of water. The SCP-2735 instances then demonstrated body language believed to represent extreme agitation, presumably due to the harmful oxygen in the air or their lack of mobility. Agents were successful in relocating the SCP-2735 subjects to their secondary containment chamber, where they were temporarily contained while their primary chamber was rebuilt with additional steel reinforcement.

Incident-2735-B: On ██/██/19██ at 3:46 am, the four SCP-2735 instances again displayed heightened bioluminescent activity. Due to similarities with behaviour prior to Incident-2735-A, Foundation agents were alerted and ordered to enter the SCP-2735 primary container. Before agents were able to arrive, the four SCP-2735 instances began to again propel themselves towards a location on the wall of their chamber, however SCP-2735-3 stopped after two (2) minutes and moved to the southeast corner of the chamber, while SCP-2735-1 displayed similar behaviour to SCP-2735-3 once Foundation agents entered the chamber at 3:54 am. No significant damage was done to the SCP-2735 chamber, and SCP-2735-2 and SCP-2735-4 were successfully restrained by Foundation agents until they ceased aggressive behaviour.

Incident-2735-C: On ██/██/20██, at 12:56 pm, SCP-2735-4 began to attempt to breach containment in a fashion similar to previous incidents, though the other SCP-2735 instances remained idle. After Incident-2735-B, SCP-2735''s special containment procedures were updated to include four (4) Foundation agents in diving gear and body armour posted outside the container, and thus the incident was responded to immediately and SCP-2735-4 was restrained without incident.

Incident-2735-D: On ██/██/20██, at 5:41 am, heightened bioluminescent behaviour was observed from both SCP-2735-2 and SCP-2735-4. Due to bioluminescent events from SCP-2735-2 and SCP-2735-4 without a follow up containment breach attempt, this behaviour was not considered significant, and thus no agents entered the chamber. Roughly five (5) minutes after this was noted, SCP-2735-4 propelled itself towards SCP-2735-2. SCP-2735-4 attached itself to SCP-2735-2 using its grasping appendages and began to repeatedly throw SCP-2735-2 towards the chamber''s wall.

The four posted agents then entered the chamber, but were repeatedly repulsed by SCP-2735-4. SCP-2735-1 and SCP-2735-3 moved to a far corner of the room and ceased bioluminescent activity at this time. Following this, SCP-2735-4 began to use its appendages to tear at SCP-2735-2''s skin. At 5:52 am, two (2) additional agents entered the chamber and began to assist the initial four agents. The agents were successful in restraining SCP-2735-4, but not before it had succeeded in dealing significant amounts of bodily harm to SCP-2735-2.

Following the incident, SCP-2735-4 was temporarily relocated to the secondary containment chamber, while SCP-2735-2 was examined by Foundation doctors. SCP-2735-2 was confirmed to be clinically dead four (4) hours after Incident-2735-D began. Fourteen (14) days after Incident-2735-D began, SCP-2735-4 was transferred to its current chamber, and the four agents assigned to SCP-2735 were reassigned to guard SCP-2735-4 specifically.

Incident-2735-E: On ██/██/20██, at 10:23 am, SCP-2735-4 began propelling itself towards the wall of its containment chamber. While repeated incidents had proven that SCP-2735-4 was incapable of actually breaching containment using this method, agents entered the chamber and restrained SCP-2735-4 to prevent it from harming itself in the attempt. Foam padding was added to the walls of SCP-2735-4''s chamber to prevent it from accidentally harming itself.

Incident-2735-F: On ██/██/20██, at 10:45 pm, SCP-2735-4 began to use its appendages to tear at its own flesh. Agents were successful in restraining it. A modified electronic shock collar was secured around SCP-2735-4''s upper body to deter this behaviour in the future.

Footnotes

1. A full list of the species cultured within SCP-2735''s containment chamber can be found in Document 2735-Gimel